Conventionally, in various kinds of electronic components, the following etching method has been known as a method for forming a wiring and an electrode on a surface of a semiconductor substrate or a glass substrate.
First, an aluminum film or an aluminum alloy film serving as a material of the wiring and the electrode (base material) is formed on the substrate. Then, a photosensitive resin is applied onto the surface by a photolithography method, and exposure and development are performed to form a pattern mask.
Then, the aluminum film or the aluminum alloy film is etched by use of the pattern mask. Thus, the wiring and the electrode having a desired pattern can be formed on the aluminum film or the aluminum alloy film.
By the way, according to the semiconductor device and the liquid crystal display device, the wiring and the electrode provided in the above device are strongly required to be miniaturized and have a high performance in recent years as a product is increasingly required to be miniaturized and have high performance. Thus, accordingly, in a technical field in which multiple stratification has been progressed, in order to respond to the multiple stratification, it is strongly desired to control a sectional shape of the wiring to have a configuration (forward tapered configuration) in which an angle (referred to as the taper angle hereinafter) formed between a side surface of the etched wiring and a surface of a base material (an insulation layer or a substrate, for example) is less than 90°.
Thus, since the wiring material has to be low in resistance along with the high density and miniaturization of the pattern in recent years, aluminum or an aluminum alloy is widely used.
In addition, when the multilayered wiring is installed, aluminum or the aluminum alloy is used as a material of a lower-layer wiring to reduce a signal delay. Then, in order to electrically insulate an upper-layer wiring from the lower-layer wiring, an insulation layer is formed on the lower-layer aluminum wiring or aluminum alloy wiring by some sort of method, and then, an aluminum wiring or aluminum alloy wiring is formed thereon as the upper-layer wiring.
Here, it is necessary to control a sectional configuration of the wiring of the lower-layer aluminum wiring or aluminum alloy wiring to have the forward tapered configuration in order to improve the coverage of the insulation layer formed thereon.
In this case, as the controllability of the sectional configuration of the lower-layer aluminum wiring or aluminum alloy wiring is important, when the sectional configuration of the wiring cannot be the forward tapered configuration or when the taper angle θ of the wiring is out of a desired range, the upper-layer aluminum wiring or aluminum alloy wiring could be disconnected or the upper-layer wiring and the lower-layer wiring could be shorted electrically through a crack generated in the insulation layer, and the problem is that reliability is lowered.
By the way, in the case where the wiring having the tapered configuration is formed by etching, the wiring having the forward tapered configuration can be formed by etching the aluminum film or aluminum alloy film by use of a water solution of a phosphoric acid/a nitric acid/an acetic acid as an etching liquid in general.
For example, when the etching is performed by use of a mixture liquid in which a volume ratio of the phosphoric acid:the nitric acid:the acetic acid:water is 16:2 to 8:2:1 with a mask having superior adhesiveness with the metal film that is formed in such a way that a resist as the mask is exposed and developed to be patterned into a predetermined wiring configuration and then baked (post-baking operation) at a baking temperature at which the sufficient adhesiveness with the metal film can be provided, the angle (taper angle) θ formed between the side surface of the wiring and the base material (such as the insulation layer or the substrate) on which the wiring is formed is close to 90° (perpendicular) without exceeding 90°.
However, when the baking temperature is lower than the appropriate temperature, since the adhesiveness of the mask with the metal film is insufficient, the etching liquid enters into an interface between the resist and the metal film. As a result, since the metal film is etched from its upper surface also, it is reported that the angle formed between the side surface of the wiring and the upper surface of the wiring is increased, and the wiring having a one-stage tapered configuration in which the side surface of the wiring is moderately sloped is formed. When the concentration of the nitric acid is additionally increased in the etching liquid, it is reported that the taper angle is decreased (refer to patent document 1).
Meanwhile, the concentration of the nitric acid is low, a one-stage tapered configuration having a large taper angle is formed, but when the concentration of the nitric acid is increased, the etching rate of the interface between the resist and the metal film is increased, so that the wiring has a two-stage forward tapered configuration having a first stage having a small taper angle formed on the interface side between the resist and the metal film and a second stage having a large taper angle formed on the side closer to the substrate. When the concentration of the nitric acid is additionally increased, the wiring having a one-stage forward tapered configuration having a small inclination is formed (refer to patent document 2 and a patent document 3).
However, when the concentration of the nitric acid is increased in the etching liquid, although the etching rate of the aluminum film or the aluminum alloy film is increased, the controllability of the etching is lowered and it is difficult to provide the wiring having the tapered configuration with high controllability.
In addition, when the concentration of the nitric acid is high in the etching liquid as a mixture of the phosphoric acid/the nitric acid/the acetic acid/water, although it is recognized that the resist is damaged by the nitric acid and the crack is generated in the resist surface, the crack is limited to the resist surface and it is reported that an etching notch is not recognized in the metal surface (refer to the patent document 2).
Furthermore, it is reported that the contraction of the resist due to the etching liquid is not progressed beyond a certain level (refer to the patent document 3).
However, in the case where the concentration of the nitric acid is high, when the resist surface is observed by a scanning electron microscope (SEM) after the etching, it is confirmed that the resist surface is cracked, and the etching trace due to the bleeding of the etching liquid (referred to as the “resist bleeding” hereinafter) is generated in the interface between the resist and the metal film inside the etched surface, that is, in the place in which the etching is not performed. Thus, when the phenomenon of the resist bleeding is generated, the metal film surface covered with the resist is etched and becomes uneven, and the problem is that the desired configuration cannot be provided.
In addition, it is required to find a method for forming a high-quality metal film having a flat and smooth film surface with no surface roughness after the etching along with the miniaturization of a semiconductor process. As an attempt to improve the condition of the metal film surface after the etching by adding an additive agent to the etching liquid, for example, an etching liquid composition in which a trialkylamine oxide surface-active agent is added to an etching liquid containing the phosphoric acid/the nitric acid/the acetic acid/water as its main components is proposed to prevent the etching from being hindered and the smoothness of the etched surface from being damaged due to bubbles attached onto the metal film surface in the etching process, and to prevent hydrogen generated when the metal film is etched by the nitric acid, from attaching on the metal film surface (in a patent document 4, for example). In addition, in order to improve fine processability of the etching liquid, it is known that a surface-active agent is added to improve wetting properties (in a patent document 5, for example).
However, according to the patent documents 4 and 5, an idea to form the metal film having the tapered configuration having the high-quality metal surface superior in smoothness with no surface roughness is not disclosed in particular.
In addition, an etching liquid to which alkyl sulfuric acid ester or a perfuluoroalkenyl phenyl ether sulfonic acid and a surface-active agent as their salt is added to an etching liquid containing the phosphoric acid/the nitric acid/the acetic acid/water as its main components is disclosed (in a patent document 6). However, according to the technique disclosed in the patent document 6, since the surface-active agent is used, and the surface-active agent contains its solvent, the surface-active agent and the solvent are oxidized by the etching liquid, and the problem is that the composition of the etching liquid is likely to be changed and the etching rate is also changed.
Furthermore, although there is a description about a low taper angle (not more than 20°), there is almost no description about a method for controlling the tapered configuration to be a desired configuration and measures against the resist bleeding.
As described above, it is required to provide the etching liquid composition capable of controlling the taper angle with high accuracy, and forming the metal film having the forward tapered configuration having the high-quality etched surface having a superior flatness and smoothness properties with no resist bleeding and no surface roughness.
Patent Document 1:
    Japanese Unexamined Patent Publication No. 7-176525Patent Document 2:    Japanese Unexamined Patent Publication No. 6-122982Patent Document 3:    Japanese Unexamined Patent Publication No. 2001-77098Patent Document 4:    Translation of PCT Application No. 4-506528Patent Document 5:    Japanese Unexamined Patent Publication No. 2003-49285Patent Document 6    Japanese Unexamined Patent Publication No. 2005-162893